Xylitol is industrially produced by a chemical reduction of hemicellulose hydrolysate prepared from plant materials such as birch and corncob, etc, or by a biological conversion of the hydrolysate using a microorganism. The chemical reduction, however, not only is difficult to separate and purify xylitol or xylose from other hydrolysates produced from hemicellulose and gives as low yield as 50-60% but also has risks of undergoing a reaction at high temperature and high pressure using alkali and waste problem.
One of the alternative biological methods which are expected to have high price competitiveness compared with the conventional chemical methods is the attempt to produce xylitol using a renewable resource containing a required amount of sugar based on a biological procedure. Although this method is expected to reduce production costs and enables recycling of resources, there is still a long way to go to establish a method of producing xylitol using such a renewable resource based on a biological method. Studies are undergoing to develop a highly efficient saccharification process using a fibrous biomass. But they are all focused on soft materials such as a straw and a corn stover.
Biomass is a reusable organic material extracted from energy crops and trees, agricultural products and forage crops, agricultural wastes and remnants, forestry wastes and debris, water plants, animal excrements, municipal wastes and other various wastes. It also indicates organic components of wood, plants, agricultural forestry byproducts, municipal wastes and industrial wastes which have been used as an energy source.
Among many natural fibrous biomasses, plants (leaves, stems and roots) are composed of three major components of cellulose, hemicellulose and lignin and other minor resins. From the decomposition or conversion of such components, a renewable resource, which is fibrous hydrolysate having high xylose content can be prepared. During the xylose production, arabinose can also be additionally obtained. To separate or decompose the above major three components, bonds among them have to be first disrupted before the conversion.
Up to date, xylose has been produced by the steps of acid-hydrolysis of hemicellulose existing in wood, straw or corncob, decoloration, ion purification and crystallization. The hydrolysate obtained from the acid-hydrolysis contains xylose, arabinose and a large amount of inorganic ions, so that purification process is required to eliminate such inorganic ions.
The purification of usable sugar components including xylose from the hydrolysate has been generally performed by the following processes. A neutralizing agent is added to the hydrolysate of acid-hydrolysis to adjust pH to 3.0˜7.0 v to obtain a precipitate; the precipitated salt is separated by filtering; color materials are eliminated by using charcoal; then the hydrolysate proceeds to ion exchange resin tower filled with cation exchange resin, anion exchange resin and mixed resin in that order, resulting in the separation of usable ingredients including xylose from the hydrolysate.
In the above processes, all ions in the hydrolysate are attached on the ion exchange resin and acids and alkalis are passed through, resulting in the separation of ions and the recovery of the resin. The solution containing the usable sugar components purified from ion exchange resin tower proceeds to a separation tower filled with Na+ type chromatography separation resin in the form of sulfated polystyrene cross-linked with divinylbenzene. As a result, the fraction with xylose in high content and the fraction having high arabinose content can be obtained. The fractionated xylose and arabinose are concentrated by Brix 60˜80, followed by crystallization to give xylose crystals and arabinose crystals.
In the purification process above, precipitation is induced by adding a chemical substance that is able for form an insoluble salt with the inorganic ion. And, the precipitated salt is separated by using a filter and as a result the salt concentration is reduced. However, salt residue remaining not-filtered can form a scale during the concentration, even though it is a small amount, resulting in the decrease of productivity. According to the method using an ion exchange resin, massive ion exchange resins are required to treat such samples that have high content of total ions. And large amount of acid/alkali solution is necessarily used for the regeneration of the ion exchange resin. Accordingly, waste water containing high content of salt increases with increasing the waste water treatment costs. Therefore, an alternative technology to reduce chemicals and waste water is strongly requested.
Another exemplary purification method is ED (electrodialysis). ED is a purification method to eliminate impurities included in the reaction solution such as colloid using direct current voltage. At this time, an ion-exchange membrane is generally used.
The conventional ED had an economical limitation in industrial applicability because this method requires high energy cost and an expensive ion exchange membrane. However, since 1980s, approximately 50 ion exchange membranes have been developed by many companies including Asahi Chemical, Asahi Glass and Tokuyama Co. of Japan and Ionics and Dupont of USA, reducing high economic costs. There are also many patent applications in relation of ED (Recovering method of organic acids (Application No: 98-0053421), Production methods of lysine-HCl (Application No: 98-0011107), Separation and purification methods for phenylalanine by electrodialysis (Application No: 99-0001349), Recovery method of lactic acid by electrodialysis process (Application No: 00-0028758), Method for purification of amino acid containing solutions by electrodialysis (Application No: 02-7005661), etc).
In general, an organic material can be burned because of carbon (C) therein, and any substance can be used as a raw material for the production of the active carbon as long as it can be burned. Representative raw materials for the production of active carbon are wood, lignite and anthracite, etc, and active carbon is produced by carbonizing them to charcoal. The charcoal is mainly composed of carbon resulted from the incomplete oxidation during carbonization of wood, and the charcoal varies from the kind of wood and temperature of burning. The major wood materials for charcoal are exemplified by an oak, a bamboo, a broadleaf tree, a palm tree, a coconut, etc, and particularly the charcoal made by an oak has been known to have better treatment effect on water purification, cleaning, fuel and garden plants, compared with other charcoal produced from a broadleaf tree, a bamboo, a palm tree or a coconut.
The two most important processes for the production of an active carbon are the carbonization process and activation process. The carbonization process indicates the procedure in which a raw material is heated at 500˜700° C., leading to dehydration and deoxidation, and then the surface oxygen is released as the forms of water, carbon monoxide and carbon dioxide, suggesting that all the volatile ingredients are eliminated and fixed carbon is left alone. The activation process indicates the oxidation reaction of carbon occurring at 800˜1,000° C., in which the surface of a carbide is eroded and thereby micropore structure is developed in the carbide.
The patents regarding the production of charcoal using byproducts of tropical fruit biomass are exemplified by Korean Patent Publication No. 2002-0095809 (Coconut charcoal and manufacturing process of it), No. 2000-0055003 (Manufacturing process of yellow ocher charcoal), No. 10-2005-0003585 (Charcoal and manufacturing method thereof), No. 2000-0012825 (Manufacturing process of coconut shell charcoal briquette) and No. 10-2005-0031310 (Ignition coal using palm charcoal dust and manufacturing method thereof). As shown in the list, there are many reports regarding the method of preparing various pressing charcoals using palm charcoal dust as a major raw material, but there have been no reports on the preparation of a high value active carbon by extracting xylose from the byproducts of tropical fruit biomass to produce charcoal using the remainders.
One problem of the conventional precipitation method is the reduced productivity owing to the scale formation. Another problem is the production of lots of waste water and the high price for the waste water treatment. Precisely, the inorganic salts and organic acids included in the hydrolysate of acid-hydrolysis resulted from the acid treatment can be eliminated by using an ion exchange resin because they have electrical charge, but to eliminate such ions rich in the hydrolysate, resin regeneration is required frequently and thereby massive acid/alkali waste water is generated. And the cost for the treatment of such waste water is very high.